In this three-part lesson, students learn about natural selection, the mechanism that drives evolution. They begin by discussing the evolution of the eye and how even a complex organ can evolve through natural selection. Then they divide into groups to learn about genetic variation, adaptation, and sexual selection and report their findings back to the class. Finally, students analyze data to determine how the beak length of Galápagos finches evolves according to environmental factors. This lesson contributes or builds toward the goals of the unit as a whole by now looking at evolution on a larger scale. They will now be examining topics that effect their lives more directly. They will be learning a lot about how they are the way they are, which is often more appealing to students. This lesson really ties all the previous lessons together by applying it to real life situations.
Objectives
Define natural selection
Explain the role genetic variation, adaptation, and sexual selection play in natural selection
Interpret graphical data
Identify patterns of evolution
Explain how speciation occurs
Necessary Time
Three class periods
The Lesson
Day 1: Evolution of the Eye
1. Show the Evolution of the Eye video and have students read the corresponding backgrounder.
2. I will then go over the agenda for the day and explain that today's lesson is important because they will be able to use what we have been talking about relate it to their real life. Next I will share with my class the following quote from Darwin's On the Origin of Species:
Organs of Extreme Perfection and Complication
To suppose that the eye with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest degree. When it was first said that the Sun stood still and the world turned round, the common sense of mankind declared the doctrine false; but the old saying of Vox populi, vox Dei, as every philosopher knows, cannot be trusted in science. Reason tells me, that if numerous gradations from a simple and imperfect eye to one complex and perfect can be shown to exist, each grade being useful to its possessor, as is certainly the case; if further, the eye ever varies and the variations be inherited, as is likewise certainly the case; and if such variations should be useful to any animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperable by our imagination, should not be considered as subversive of the theory.
3. Discuss with the class the following topics:
Why were people resistant to the idea that the eye evolved through natural selection?
What evidence can you give to show that evolution did occur through natural selection? (For example, some animals alive today have simpler stages of the eye; Nilsson's work shows how the evolution could take place through small changes, etc.)
Why has the flatworm not evolved a more complex eye with a lens?
Why did Darwin compare his theory of natural selection to Copernicus's theory that Earth orbited the Sun?
4. Lecture on Population in Genetics and Evolution, making sure to explain:
Populations, not individuals, evolve
Changes in genetic equilibrium
Natural selection acts on variations
Day 2: Components of Natural Selection
1. I will go over the agenda for the day and explain that today's lesson is important because they will have the opportunity to explore components of natural selection in groups and learn from and with each other. I will tell them that this builds upon the unit because now they can learn about critical components to make evolution happen. If none of the topics didn't exist, then evolution very well may not exist! I will then divide the class into three groups. Assign each group a different component of natural selection: genetic variation, adaptation, and sexual selection.
Have the genetic variation group watch the The Red Queen video and the A Mutation Story video and visit the Microbe Clock Web activity. Tell students to take notes as they view the segments. Then instruct them to write short summaries and to prepare a short presentation for the class about the factors that provide genetic variation (sexual reproduction, mutation), why genetic variation is important for the survival of a species, and how variation makes natural selection possible. Tell students to cite specific examples from the sources they viewed.
Have the adaptation group view the Evolution of Camouflage video, the Shape of Trees: The Frustration Principle image, and Mimicry: The Orchid and the Bee and read the corresponding backgrounders. Tell students to take notes on the segments and readings, then write paragraph summaries and prepare a short presentation for the class about the role adaptation plays in the process of natural selection. Ask them to consider external influences such as predators, competitors for food, and access to mates (or, in the orchid's case, pollinators).
Have the sexual selection group view the Tale of the Peacock video, the The Mating Game Web feature, and Sweaty T-shirts and Human Mate Choice video. Tell students to take notes while they view the videos and try out the Web feature. Tell students to take notes on the segments and readings, then write paragraph summaries and prepare a short presentation for the class about the role sexual selection plays in the process of natural selection. Ask them to consider why male competition and female choice have evolved as a selection means in many species and the importance partner selection plays in genetic diversity.
2. Have the groups do the presentations and talk about the topics to the class while I write notes on the board and add to and/or correct statements made by the students. I will make sure the following concepts are covered:
Physical barriers can prevent interbreeding
Reproductive isolation can result in speciation
A change in chromosome numbers and speciation
Speciation Rates
Day 3: Interpreting the Data
1. I will go over the agenda for the day and explain that today's lesson is important because they will be able to look at real data taken from nature and be able to apply what they have learned. By applying what they know, they will better understand the material and actually be able to use their knowledge. I will then handout the Finch Beak Data Sheet to the class. Read the backgrounder in class and talk about the importance of the Grants' work. Ask students to identify specific data (from the data sheet) that supports each of the following claims:
Some of these variable traits are heritable (passed on to offspring).
More offspring are produced than can survive because of limited resources such as food and nesting sites.
Individuals with advantageous traits are more likely to survive and reproduce. Print the Answer Key to Darwin's Finches (PDF) for your own reference.
2. Discuss the following questions as a class:
How do you know that finches' beak length is heritable?
How did the finch population change from before the drought to after?
Why do you think the average beak length of the birds increased?
3. Expand the discussion on finches to include the topic of adaptive radiation. Show the Adaptive Radiation: Darwin's Finches graphic. Talk about how environmental influences on the Galápagos Islands led to the evolution of thirteen distinct species of finches.
Overview
In this three-part lesson, students learn about natural selection, the mechanism that drives evolution. They begin by discussing the evolution of the eye and how even a complex organ can evolve through natural selection. Then they divide into groups to learn about genetic variation, adaptation, and sexual selection and report their findings back to the class. Finally, students analyze data to determine how the beak length of Galápagos finches evolves according to environmental factors. This lesson contributes or builds toward the goals of the unit as a whole by now looking at evolution on a larger scale. They will now be examining topics that effect their lives more directly. They will be learning a lot about how they are the way they are, which is often more appealing to students. This lesson really ties all the previous lessons together by applying it to real life situations.Objectives
Necessary Time
The Lesson
Day 1: Evolution of the Eye
1. Show the Evolution of the Eye video and have students read the corresponding backgrounder.2. I will then go over the agenda for the day and explain that today's lesson is important because they will be able to use what we have been talking about relate it to their real life. Next I will share with my class the following quote from Darwin's On the Origin of Species:
To suppose that the eye with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest degree. When it was first said that the Sun stood still and the world turned round, the common sense of mankind declared the doctrine false; but the old saying of Vox populi, vox Dei, as every philosopher knows, cannot be trusted in science. Reason tells me, that if numerous gradations from a simple and imperfect eye to one complex and perfect can be shown to exist, each grade being useful to its possessor, as is certainly the case; if further, the eye ever varies and the variations be inherited, as is likewise certainly the case; and if such variations should be useful to any animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperable by our imagination, should not be considered as subversive of the theory.
3. Discuss with the class the following topics:
4. Lecture on Population in Genetics and Evolution, making sure to explain:
Day 2: Components of Natural Selection
1. I will go over the agenda for the day and explain that today's lesson is important because they will have the opportunity to explore components of natural selection in groups and learn from and with each other. I will tell them that this builds upon the unit because now they can learn about critical components to make evolution happen. If none of the topics didn't exist, then evolution very well may not exist! I will then divide the class into three groups. Assign each group a different component of natural selection: genetic variation, adaptation, and sexual selection.
2. Have the groups do the presentations and talk about the topics to the class while I write notes on the board and add to and/or correct statements made by the students. I will make sure the following concepts are covered:
Day 3: Interpreting the Data
1. I will go over the agenda for the day and explain that today's lesson is important because they will be able to look at real data taken from nature and be able to apply what they have learned. By applying what they know, they will better understand the material and actually be able to use their knowledge. I will then handout the Finch Beak Data Sheet to the class. Read the backgrounder in class and talk about the importance of the Grants' work. Ask students to identify specific data (from the data sheet) that supports each of the following claims:
2. Discuss the following questions as a class:
3. Expand the discussion on finches to include the topic of adaptive radiation. Show the Adaptive Radiation: Darwin's Finches graphic. Talk about how environmental influences on the Galápagos Islands led to the evolution of thirteen distinct species of finches.
4. Lecture on Patterns of Evolution discussing:
Materials Needed
Multimedia Resources